Ubuntu 18.04 keyboard and mouse not working at login screen

this is now i solved my issue.

1. reached the root shell and logged in by pressing shift key then selecting advanced option.
2. pressed ctrl + alt + f2/f3/f4/f5 .it asked for login details but nothing worked. gave me this error: ERROR : ****** incorrect details. pam_nologin(8)
3. ctrl + d to close root shell and then click clean then dpkg then network and back to root . this time it worked ctrl + alt + f3.
4. asked for login details and this time it did not give me this error: ERROR : pam_nologin(8) kind of error. i was able to login to user terminal.
5. as i had purged my nvidia drivers. i did these things :

6. sudo add-apt-repository ppa:graphics-drivers/ppa sudo ubuntu-drivers devices sudo ubuntu-drivers autoinstall #this installed nvidia-418 for me on its own. sudo apt-get update --fix-missing sudo apt-get install xserver-xorg-input-all sudo apt-get update && sudo apt-get upgrade -y sudo shutdown -r now this is to shutdown and restart.

IT WORKED. i was able to login to my system and then still the keyboard and mouse was working and i checked the graphics card info. it was the latest driver. dont know what had happened before. but this small weird error took my three days and good two nights.

maybe it is just because of Xserver module lost，I fix it by this： Ctrl + Alt + F1 into the tty mode and

 sudo apt install xserver-xorg-input-all